Optical stylus for optical position determination device

Abstract

The invention relates to an optical stylus ( 10 ) for an optical position determination device ( 1 ) comprising a position-encoded surface ( 50 ) having different position-encoding patterns ( 52 ). The optical stylus ( 10 ) comprises a housing ( 12 ) including: an image sensor ( 20 ) for capturing at least one image of any position-encoding pattern ( 52 ) of the position-encoded surface ( 50 ): an optical arrangement ( 15 ) comprising a dynamic optical element ( 16 ) configured to be electrically actuated in order to adjust the focal length of the optical stylus ( 10 ) as a function of a separation distance (D) between a reference point of the optical stylus ( 10 ) and the position of any position-encoding pattern ( 52 ) to have a substantially in-focus position-encoding pattern ( 52 ) corresponding to the position of the optical stylus ( 10 ), and a control unit ( 24 ) to control the dynamical optical element ( 16 ). The optical stylus further comprises a distance measurement sensor ( 32 ) to measure the separation distance (D). The control unit ( 24 ) is adapted for actuating the dynamic optical element ( 16 ) to adjust the focal length of the optical stylus ( 10 ) as a function of the output signal of the distance measurement sensor ( 32 ).

The invention claimed is: 
     
       1. An optical stylus for an optical position determination device comprising a position-encoded surface having different position-encoding patterns, the optical stylus comprising:
 an image sensor for capturing at least one image of any position-encoding pattern of the position-encoded surface, 
 an optical arrangement comprising a dynamic optical element configured to be electrically actuated in order to adjust the focal length of the optical stylus as a function of a separation distance (D) between a reference point of the optical stylus and the position of any position-encoding pattern to have a substantially in-focus position-encoding pattern corresponding to the position of the optical stylus, 
 a control or processing unit configured to actuate the dynamical optical element to adjust the focal length of the optical stylus as a function of a control signal, and 
 an aperture or a window at a distal end of the optical stylus, 
 wherein the optical stylus is adapted to identify any substantially in-focus encoding-pattern of the position-encoded surface independently of said separation distance (D) for position determination of the optical stylus relative to said surface, 
 wherein the optical stylus further comprises a distance measurement sensor to output said control signal as a function of said separation distance (D), 
 wherein the control or processing unit is configured to control the dynamic optical element according to either a 3D mode or a 2D mode, and 
 wherein, in said 3D mode, an electrical signal is applied to the dynamic optical element, the electrical signal varying as a function of said separation distance (D), to vary the focal length of the optical stylus accordingly. 
 
     
     
       2. The optical stylus according to  claim 1 , wherein
 in said 2D mode, wherein no varying electrical signal is applied to the dynamic optical element such that the focal length of the optical stylus remains constant and any encoding-pattern is substantially in-focus when the distal end of the optical stylus is in contact or within a range up to 5 mm to said position-encoded surface. 
 
     
     
       3. The optical stylus according to  claim 2 , wherein said control or processing unit is configured to switch the optical stylus between said 2D mode and 3D mode as a function of the output signal of the distance measuring sensor. 
     
     
       4. The optical stylus according to  claim 2 , further comprising a functional button electrically connected to the control or processing unit to switch the optical stylus between the 2D mode and the 3D mode. 
     
     
       5. The optical stylus according to  claim 2 , further comprising a pressure sensor located in the tip of the stylus, wherein said control or processing unit is configured to switch the optical stylus between said 2D mode and 3D mode as a function of the output signal of the pressure sensor. 
     
     
       6. The optical stylus according to  claim 1 , wherein the distance measurement sensor is a time-of-flight sensor. 
     
     
       7. The optical stylus according to  claim 1 , wherein the dynamic optical element is either of the two following elements:
 a liquid or polymer lens electrically actuable to adjust said focal length, 
 a fixed-focus lens mounted on an actuator configured to shift the fixed-focus lens along an optical path of the optical stylus to adjust said focal length, the actuator being preferably a piezoelectric element. 
 
     
     
       8. The optical stylus according to  claim 1 , further comprising at least one or both selected from the group consisting of: a light emitting unit adapted to illuminate any position-encoding pattern, and an Inertial Measurement Unit (IMU). 
     
     
       9. The optical stylus according to  claim 1 , further comprising a battery and an electrical circuit including the processing unit, the image sensor and a memory, the battery being configured to power the electrical circuit, wherein the memory stores an image processing and/or a pattern recognition algorithm for determining the position of the optical stylus relative to the position-encoded surface. 
     
     
       10. The optical stylus according to  claim 1 , further comprising at a distal end a specific shape for writing, painting or calligraphy application, said specific shape being in the form of a brush comprising a bundle of filaments, another flexible tip or a pen-like tip, wherein said aperture or said window is located at the distal end of the optical stylus such that an image of both said specific shape and the corresponding position-encoding pattern may be captured together by the image sensor. 
     
     
       11. An optical position determination device comprising the optical stylus according to  claim 1 , and a host device comprising a screen, and a position-encoded surface having different position-encoding patterns, wherein the host device is configured to receive data from the optical stylus to generate on the screen a trace following the motion of the optical stylus relative to the position-encoded surface. 
     
     
       12. The optical position determination device according to  claim 11 , wherein the position encoded surface is an integral part of the host device or is a stand-alone position encoded surface. 
     
     
       13. The optical position determination device according to  claim 11 , wherein the position encoded surface is made of a flexible material applied on the screen top surface of the host device. 
     
     
       14. The optical position determination device according to  claim 11 , wherein the different position-encoding patterns of the position-encoded surface are transparent in the visible range of the light spectrum. 
     
     
       15. The optical position determination device according to  claim 12 , wherein the host device or the stand-alone position encoded surface comprises one light or more light sources, configured to emit light outside the visible range of the light spectrum and arranged below the position-encoded surface to back illuminate each of the position-encoding patterns. 
     
     
       16. A method of determining the position of an optical stylus relative to a position-encoded surface comprising different position-encoding patterns, the optical stylus comprising:
 an image sensor for capturing at least one image of any position-encoding pattern of the position-encoded surface, 
 an optical arrangement comprising a dynamic optical element configured to be electrically actuated, 
 a distance measurement sensor for measuring a separation distance (D) between a reference point of the optical stylus and the position of any position-encoding pattern, and 
 a control or processing unit to control the dynamic optical element, 
 wherein the control or processing unit is configured to control the dynamic optical element according to a 3D mode or a 2D mode, and wherein, in said 3D mode, the method comprises the steps of:
 a. holding the optical stylus in the direction of the position-encoded surface, 
 b. applying an electrical signal to the dynamic optical element, wherein the electrical signal is varying as a function of said separation distance (D) measured by said distance measurement sensor, and actuating the dynamic optical element to adjust the focal length of the optical stylus as a function of said electrical signal, 
 c. acquiring by the image sensor the optical signal of the image formed by the optical arrangement of a substantially in-focus position-encoding pattern of the position-encoded surface, and 
 d. processing the optical signal to determine the position of the optical stylus relative to the position-encoded surface. 
 
 
     
     
       17. The method according to  claim 16 , wherein the optical stylus further comprises a gyroscope and/or an accelerometer, wherein the position of the optical stylus is computed based on
 both the optical signal acquired by the image sensor and data acquired by said gyroscope and/or accelerometer, or 
 data acquired by said gyroscope and/or accelerometer. 
 
     
     
       18. The method according to  claim 16 , wherein the optical stylus further comprises a light emitting unit, wherein the light intensity of the light emitting unit is controlled as a function of the output signal of the distance measurement sensor. 
     
     
       19. The method according to  claim 16 , wherein data representing image perspective of any of said position-encoding pattern captured by the image sensor are processed by the processing unit of the optical stylus which runs a computer vision algorithm for determining the position of the optical stylus prior sending to the host device position-related data for displaying a trace on the screen following the relative movement of the optical stylus relative to the position-encoded surface. 
     
     
       20. The method according to  claim 19 , wherein the hue, stroke width and/or shape of said trace is modulated as a function of any or a combination of two or more of the following parameters of the optical stylus: speed, acceleration, orientation and tip pressure on the position-encoded surface.